Control for a hydrostatic power train

ABSTRACT

The invention concerns a control for a hydrostatic power train ( 1 ) comprising a hydraulic pump ( 2 ) which is connected, via a first main pipe and a second main pipe ( 7, 8 ), to a first hydromotor unit ( 5, 5 ′) driving a front axle and to a second hydromotor unit ( 6, 6 ′) driving a rear axle. The first and second hydromotor units ( 5, 5′, 6, 6 ′) can be adjusted in terms of their displacement via a first and a second variation device ( 30, 31, 30′, 31 ′) respectively. A direction of travel is defined as forward movement (F) or reverse movement (R) by a position of an operating lever ( 37 ). The first and the second variation devices ( 30, 31, 30′, 31 ′) are controlled by a control valve ( 32, 32 ′) which takes up a first control position upon a forward movement (F) determined by the position of the operating lever ( 37 ) and which takes up a second control position upon reverse movement (R) determined by the operating lever ( 37 ). In the first control position, the first variation device ( 30, 30 ′) is controlled such that the first motor unit ( 5, 5 ′) is adjusted for a smaller displacement and, in the second control position, the second variation device ( 31, 31 ′) is controlled such that the second motor unit ( 6, 6 ) is adjusted for a smaller displacement.

The invention concerns a controller for a hydrostatic traversingmechanism.

Hydrostatic traversing mechanisms, in which two hydraulic motors areconnected to a hydraulic pump and the hydraulic pump is driven by adriving motor, are known as traversing mechanisms of working machinessuch as road rollers. In such a system, in which one hydraulic motoreach is assigned to the front and rear axles, to adapt the torquedistribution of the individual motors to the conditions of use, e.g.uphill and downhill, various systems for traction control are known.

In DE 101 01 748 A1, for instance, a system in which signals frompressure sensors, which are arranged in the pressure-side andinduction-side main duct, are fed to an electronic control unit, isproposed. On the basis of changes of the pressure signals and changes ofthe position of a driving lever, the electronic control unit determinesthe present driving situation of the vehicle. For this purpose, athreshold value which is corrected depending on changes of the positionof the driving lever is used, so that different driving situations canbe clearly distinguished from each other. If one of the pressure sensorsdetermines a pressure value which exceeds the corrected threshold value,the driving situation which the electronic control unit determines isused to send an electrical signal for adjustment towards a lowerabsorption volume to an adjustment device of the up-side hydraulicmotor.

The system which is proposed in DE 101 01 748 A1 has the disadvantagethat the cost of construction is relatively great. Thus not only arepressure sensors required in both main ducts, but also an electroniccontroller, which is capable of storing changes of the position of thedriving lever at least for a short time, so that it can not onlyevaluate an instantaneous actual value, but also include the change ofthe driving lever position in the determination of the drivingsituation.

Also, from DE 196 38 421 A1 a traction controller, in which a gradientsensor is used to prevent an unwanted adjustment of a down-sidehydraulic motor in the direction of smaller pivoting angles, is known.The system is based on a traction controller, which detects differingwheel circumference speeds on the front and rear axles on the basis ofr.p.m. sensors, and by adjusting the absorption volume adjusts ther.p.m. of the corresponding hydraulic motor. In this case the situationwhich can occur is that the wheel circumference speed of the down-sideaxle during downhill motion is less than the wheel circumference speedof the up-side axle, because of the slip which occurs. Because of theregulating intervention of the traction controller, this would result inan adjustment of the down-side hydraulic motor in the direction of asmaller pivoting angle, to raise the r.p.m. of the hydraulic motor,which however causes a reduction of the moment. To maintain the brakingmoment during downhill motion, the information of a gradient sensor isused, to suppress the control commands which the traction controllergives to the adjustment device of the hydraulic motor and thus toprevent the adjustment of the hydraulic motor in the direction of asmaller pivoting angle. The gradient sensor therefore prevents anadjustment of the pivoting angle of the hydraulic motor.

The system which is known from DE 196 38 421 A1 has the disadvantagethat the traction controller intervenes only when a slip has alreadyoccurred. On the other hand, reduction of the transmitted torque to oneof the axles before a slip occurs on one of the axles is not provided.

The invention is based on the object of creating a controller for ahydrostatic traversing mechanism. With this controller, a preventiveadjustment of hydraulic motor units takes place in a simple way, to actagainst the inclination to form a slip.

The object is achieved by the controller according to the invention, fora hydrostatic traversing mechanism with the features of claim 1 andalternatively of the subordinate claims 2 and 13.

In the case of the controller according to the invention for thehydrostatic traversing mechanism, it is advantageous that drive torquesare differentially distributed to the front and rear axles of thevehicle on the basis of a simple signal. According to claims 1 and 2,this simple signal is either the direction of motion which is given viathe driving lever or the direction of inclination of the vehicle, whichis determined by an inclination sensor. Corresponding to the directionof motion or the determined inclination of the vehicle, a control valve,through which, by means of a variation device which is provided on theappropriate hydraulic motor unit, a hydraulic motor unit is adjusted inthe direction of smaller absorption volume, is operated. Through theadjustment of the hydraulic motor unit in the direction of smallerabsorption volume, the torque which can be transmitted to thecorresponding axle is reduced, thus acting against the occurrence ofslip.

In the case of the subject of claim 13, instead of an electrical signalthe sign of the pressure difference between a first and a second mainduct is used to apply pressure to the variation device of the relevanthydraulic motor unit by means of a control valve unit, in such a waythat one of the two hydraulic motor units is adjusted in the directionof a smaller pivoting angle. Use of the sign of the pressure differencebetween the first and the second main duct has the advantage that forboth forward motion and backward motion, the hydraulic motor unit of theaxle which is oriented uphill is adjusted in the direction of smallerabsorption volume. Because of the pressure reversal in the first andsecond main ducts during downhill motion, even for a downhill motion thehydraulic motor unit which is oriented uphill is pivoted in thedirection of smaller torque, so that for downhill braking too, optimumdistribution of moment on the axles is achieved.

Advantageous extensions of the controller according to the invention arepresented in the subclaims.

It is particularly advantageous to provide, on the control valve orcontrol valve unit, an additional switching position, in which both thehydraulic motor unit of the front axle and the hydraulic motor unit ofthe rear axle are adjusted in the direction of smaller absorptionvolume, to make a higher speed of motion possible, e.g. for transport.

A further advantage is, simultaneously with the adjustment of ahydraulic motor unit in the direction of smaller torque, to adjust theabsorption volume of the other hydraulic motor unit oppositely, in thedirection of greater absorption volume, so that the sum of theabsorption volumes remains constant. For this purpose, a hydraulic motorunit consisting of several hydraulic motors, each of which has aconstant absorption volume, can be used specially advantageously. Tochange the absorption volume of such a hydraulic motor unit, one of thehydraulic motors can then be switched on or off.

According to another advantageous extension, it is provided that theabsorption volume of the hydraulic motor units is continuouslyadjustable. For this purpose, the control valve or control valve unit,as well as the control valves which are provided on each of thevariation devices, are in the form of continuously adjustable valves.Thus, particularly if an inclination sensor, which not only determinesthe existence of a downhill or uphill gradient but also its steepness,is used, a continuous shift of the ratio between the torques on thefront axle and rear axle can occur.

Preferred embodiments of the controller according to the invention for ahydrostatic traversing mechanism are shown in the drawings, and areexplained in more detail on the basis of the following description.

FIG. 1 shows a schematic representation of a hydrostatic traversingmechanism, with a first embodiment of a controller according to theinvention;

FIG. 2 shows a schematic representation of a hydrostatic traversingmechanism, with a second embodiment of a controller according to theinvention;

FIG. 3 shows a schematic representation of a hydrostatic traversingmechanism, with a third embodiment of a controller according to theinvention;

FIG. 4 shows a schematic representation of a hydrostatic traversingmechanism, with a fourth embodiment of a controller according to theinvention;

FIG. 5 shows a schematic representation of a hydrostatic traversingmechanism, with a fifth embodiment of a controller according to theinvention;

FIG. 6 shows a schematic representation of a hydrostatic traversingmechanism, with a sixth embodiment of a controller according to theinvention; and

FIG. 7 shows an example of a vehicle, with a hydrostatic traversingmechanism which is equipped with the controller according to theinvention.

A first embodiment of a controller according to the invention for ahydrostatic traversing mechanism is shown in FIG. 1. A hydrostatictraversing mechanism 1 includes a pump 2, which is driven by a primemover 3. The pump 2 is connected via a drive shaft 4 to the prime mover3. The hydrostatic traversing mechanism also includes a first hydraulicmotor unit 5 and a second hydraulic motor unit 6. The first hydraulicmotor unit 5 and the second hydraulic motor unit 6 are connected inparallel via a first main duct 7 and a second main duct 8 to the pump 2.Depending on the delivery direction of the pump 2, the hydraulic fluidis fed from the first main duct 7 via a first connecting duct 7′ to thefirst hydraulic motor unit 5, and via a second connecting duct 7″ to thesecond hydraulic motor unit 6, or, in the case of delivery in theopposite direction, from the second main duct 8 via a third connectingduct 8′ to the first hydraulic motor unit 5, and via a fourth connectingduct 8″ to the second hydraulic motor unit 6.

The pump 2 is adjustable for delivery volume, and suitable for deliveryin two directions. The delivery volume is set by an adjustment device(not shown). The adjustment device can be adjusted by signals from anelectronic control unit (also not shown). The electronic control unitpreferably also acts on the prime mover 3 and adjusts it for power andr.p.m. An auxiliary pump 9 is driven by the prime mover 3 via a section4′ of the drive shaft 4. The auxiliary pump 9 is suitable for deliveryin one direction, and its delivery volume is permanently set. On itsinduction side, the auxiliary pump 9 is connected via an induction duct10 to a tank volume 11. In a duct 12 which is connected on the pressureside to the auxiliary pump 9, a pressure relief valve 13, which relievesthe duct 12 into the tank volume 11 when a maximum pressure which isdetermined by a spring is exceeded, is provided. The duct 12 isconnected via a first feed duct 14 to the first main duct 7, and via asecond feed duct 15 to the second main duct 8.

In each of the first and second feed duct 14 and 15, a first non-returnvalve 16 and second non-return valve 17 which open in the direction ofthe first main duct 7 and second main duct 8 respectively are arranged.Parallel to the first and second non-return valve 16 and 17respectively, a maximum pressure relief valve 18 and 19, which relievesthe first main duct 7 and second main duct 8 respectively via the duct12 and pressure relief valve 13 into the tank volume 11 when a maximumpermitted pressure for the main ducts 7 and 8 is exceeded, is provided.

The first hydraulic motor unit 5 drives, for instance, a roller which isarranged on the front axle of a road roller, via a first driven shaft20. A second roller, which is arranged on the rear axle of a roadroller, is driven via a second driven shaft 21 by the second hydraulicmotor unit 6. The first hydraulic motor unit 5 and second hydraulicmotor unit 6 are preferably constructed identically, and each include afirst hydraulic motor 22 and 23 respectively and a second hydraulicmotor 22′ and 23′ respectively which is assigned to the first hydraulicmotor 22 and 23. The first and second hydraulic motor 22 and 22′ of thefirst hydraulic motor unit 5 and the first and second hydraulic motor 23and 23′ of the second hydraulic motor unit 6 are designed for driving inboth directions, and each have a constant absorption volume. Theabsorption volume of the two first hydraulic motors 22 and 23 ispreferably identical. The absorption volume of the two second hydraulicmotors 22′ and 23′ is also preferably identical. On the other hand, theabsorption volume of the first hydraulic motor 22 and second hydraulicmotor 22′, and of the first hydraulic motor 23 and second hydraulicmotor 23′, can be different.

The second hydraulic motor 22′ of the first hydraulic motor unit 5 andthe second hydraulic motor 23′ of the second hydraulic motor unit 6 areimplemented so that they can be switched on and off. To switch thesecond hydraulic motor 22′ and 23′ on and off, in each case a controlvalve 24 and 25 respectively is provided in the first hydraulic motorunit 5 and second hydraulic motor unit 6 respectively. The controlvalves 24 and 25 are held in an initial position by a control valvespring 26 and 27 respectively. On the control valves 24 and 25, acontrol surface 28 and 29 respectively, to which a control pressurewhich steers the control valve 24 and 25 respectively out of its initialposition against the force of the control valve spring 26 and 27respectively is applied, is provided.

If the control valve 24 and 25 is in its initial position, the pressuremeans which is fed out of the first main duct 7 and second main duct 8of the respective hydraulic motor unit 5 or 6 is also fed to the secondhydraulic motor 22′ and 23′. For this purpose, a first linking duct 41,which is connected via the control valve 24 in its initial position to afirst joining duct 45 and thus to an input of the second hydraulic motor22′, branches off from the first connecting duct 7′. A second terminalof the first hydraulic motor 22′ is connected via a second joining duct46, the control valve 24 in its initial position, and a second linkingduct 42 to the third connecting duct 8′. The second hydraulic motor 23′of the second hydraulic motor unit 6 is similarly connected via a thirdand fourth joining duct 47 and 48, which in the initial position of thecontrol valve 25 are connected to a third and fourth linking duct 43 and44 respectively, to the second connecting duct 7″ and fourth connectingduct 8″ respectively.

On the other hand, if the control valve 24 is in the opposite finalposition, the first and second joining duct 45 and 46 of the secondhydraulic motor 22′ of the first hydraulic motor unit 5 are connected toeach other. In this switch position of the control valve 24, the secondhydraulic motor 22′ is short-circuited, and does not contribute to thegeneration of a torque on the first driven shaft 20. Correspondingly,the third joining duct 47 and fourth joining duct 48 are connected toeach other if the control valve 25 is in the opposite final position.The control valve 24 acts with the hydraulic motor 22′ of the firsthydraulic motor unit 5 to form a first variation device 30. The controlvalve 25 acts with the hydraulic motor 23′ of the second hydraulic motorunit 6 to form a second variation device 31.

To control the first variation device 30 and the second variation device31, a control valve 32 is provided. The control valve 32 is held by acontrol valve spring 33 in a first switch position. Against the force ofthe control valve spring 33, a force can be applied to the control valve32 by an electromagnet 34. The electromagnet 34 is connected via asignal line 35 to an electronic device 36, which depending on theposition of a driving lever 37 applies a switching current to theelectromagnet 34. Via another signal line 38, the electronic device 36receives from the driving lever 37 a signal for whether the position ofthe driving lever is pointing in the direction of forward driving orbackward driving.

In the shown embodiment, the control valve 32 is in the form of a switchvalve, which depending on the signal at the electromagnet 34 switchesbetween a first and a second switch position. In the first switchposition, in which in the idle state the control valve 32 is, because ofthe control valve spring 33, the control surface 28 of the control valve24 of the first hydraulic motor unit 5 is connected via a first controlpressure duct 39 to a removal duct 40. The removal duct 40, at the endfacing away from the control valve 32, is connected to the duct 12, sothat in the first switch position of the control valve 32 the pressurein the duct 12 is applied to the control surface 28 of the control valve24 of the first hydraulic motor unit 5. The pressure which is generatedby the auxiliary pump 9 in the duct 12 is sufficient to overcome thecounter-force of the control valve spring 26, so that the control valve24 is displaced in the direction of the final position opposite theinitial position. By displacing the control valve 24 into its finalposition opposite the initial position, the first and second joiningduct 45 and 46 of the second hydraulic motor 22′ are short-circuited, sothat, as explained above, the second hydraulic motor 22′ supplies nocontribution to the torque on the first driven shaft 20.

Simultaneously, in the first switch position of the control valve 32,the control surface 29 of the control valve 25 of the second hydraulicmotor unit 6 is connected via a second control pressure duct 49 to arelief duct 50, which opens into the tank volume 11 on its side facingaway from the control valve 32. The control valve 25 of the secondhydraulic motor unit 6 is therefore, because of the force of the controlvalve spring 27, in its initial position. The control valve 25 in itsinitial position connects a third linking duct 43 to the third joiningduct 47 and a fourth linking duct 44 to the fourth joining duct 48. Thethird and fourth linking duct 43 and 44 are connected via the secondconnecting duct 7″ and fourth connecting duct 8″ to the first main duct7 and second main duct 8 respectively, so that the pressure means whichthe pump 2 conveys into one of the main ducts 7 or 8 is also conveyed tothe second hydraulic motor 23′ of the second hydraulic motor unit 6. Atorque which is generated by the hydraulic motor 23 and the secondhydraulic motor 23′ therefore acts on the driven shaft 21.

If the vehicle, for instance a road roller, moves forwards, the operatorhas steered the driving lever 37 in the direction of a forward motion F.The steering of the driving lever 37 in the direction of a forwardmotion F is transmitted via the further signal line 38 of the electronicdevice 36. In the electronic device 36, a suitable control signal forthe electromagnet 34 is generated, or a switched current, which istransmitted via the signal line 35 to the electromagnet 34, is generateddirectly. In the shown embodiment, because of this signal, no currentflows through the electromagnet 34, so that the control valve 32 is heldin its first switch position because of the control valve spring 33.

The auxiliary pump 9 is driven by the prime mover 3 via the section 4′of the drive shaft 4, and generates a pressure which is fed via theremoval duct 40 of the control surface 28 of the control valve 24 of thefirst hydraulic motor unit 5. In the embodiment shown in FIG. 1, thefirst hydraulic motor unit 5 is assigned to the front axle of the roadroller. Depending on the desired driving speed, the pump 2 generates avolume stream which is delivered into the second main duct 8, and is fedvia both the third connecting duct 8′ and the fourth connecting duct 8″to both the first hydraulic motor unit 5 and the second hydraulic motorunit 6. Because of the control pressure which is present on the controlsurface 28 of the control valve 24 of the first hydraulic motor unit 5,the first joining duct 45 and second joining duct 46 of the secondhydraulic motor 22′ of the first hydraulic motor unit 5 areshort-circuited, so that on the front axle, via the first driven shaft20, only the torque which is generated by the first hydraulic motor 22of the first hydraulic motor unit 5 is present.

On the other hand, in the case of the second hydraulic motor unit 6which is assigned to the rear axle, a higher torque, which is generatedbecause of the connected second hydraulic motor 23′ and the hydraulicmotor 23, acts on the second driven shaft 21. For this purpose, thesecond hydraulic motor 23′ of the second hydraulic motor unit 6 isconnected via the control valve 25, by being connected via the third andfourth linking duct 43 and 44 to the first main duct 7 and second mainduct 8 respectively.

Because of this unequal distribution of the torques to the front axleand rear axle of the driven vehicle, during uphill motion the axle whichis relieved of load by the inclination of the plane is driven with lessmoment. If a vehicle moves forwards up a hill, the front axle firsttends to slip. This tendency for slip to occur is counteracted by thereduction of the moment on the front axle. The described distribution ofthe torques to the front axle and rear axle is carried out preventivelyirrespective of an actually occurring uphill motion, so that even in thecase of a forward motion on the level, the torque on the front axle isreduced compared with the torque on the rear axle. The danger of errorsin recognising the driving situation is reduced by simply using thedirection of motion as the basis. The distribution of the torque infavour of the drive on the rear axle during forward motion alsocorresponds to the requirements which occur during motion on the level,since during acceleration the rear axle can transmit a higher torquethan the front axle.

In a change of direction of motion, the operator moves the driving lever37 out of the direction for forward motion F into the direction forbackward motion R. The change of direction of motion signal is in turnconverted by the electronic device 36 into a suitable signal for theelectromagnet and transmitted via the signal line 35 to theelectromagnet 34. Corresponding to the signal which is now present onthe electromagnet 34, current flows through the electromagnet 34 andswitches the control valve 32 into its second switch position. In thesecond switch position, the removal duct 40 is connected to the secondcontrol pressure duct 49, so that the pressure which the auxiliary pump9 generates is present on the control surface 29 of the control valve 25of the second hydraulic motor unit 6. Correspondingly, the first controlpressure duct 39 is now connected to the load relief duct 50. In thisway, the control surface 28 of the control valve 24 of the firsthydraulic motor unit 5 is relieved of pressure by the connection to thetank volume 11, so that the control valve 24 returns to its initialposition because of the control valve spring 26.

In the second switch position of the control valve 32, the secondhydraulic motor 23′ is consequently switched off, by the third joiningduct 47 being short-circuited to the fourth joining duct 48 by thecontrol valve 25. On the other hand, the second hydraulic motor 22′ ofthe first hydraulic motor unit 5 is connected via the first linking duct41 and second linking duct 42 to the first main duct 7 and second mainduct 8 respectively, and thus supplies a contribution to the torquewhich is available on the first driven shaft 20. Therefore, if thedriving lever 37 is steered in the direction of a backward motion, asmaller torque is generated on the rear axle than on the front axle. Inthis way, in each case a smaller torque is generated on the front axleseen in the direction of motion.

The total absorption volume remains constant in each case, because whenthe second hydraulic motor 22′ of the first hydraulic motor unit 5 isswitched on, correspondingly the second hydraulic motor 23′ of thesecond hydraulic motor unit 6 is switched off, and vice versa. By thiscompensation of the change of the absorption volume on the first orsecond hydraulic motor unit 5 or 6, control of the delivery volume ofthe pump 2 is simplified.

In FIG. 2, a second embodiment of a controller according to theinvention is shown. Identical components are given identical referencesymbols. To avoid repetitions, reference is made to the description ofFIG. 1.

In contrast to the first embodiment of FIG. 1, in the hydrostatictraversing mechanism according to FIG. 2 a first hydraulic motor unit 5′and a second hydraulic motor unit 6′, which have a first hydraulic motor55 and a second hydraulic motor 56 respectively, are provided. Theabsorption volume of the first and second hydraulic motor 55 and 56 isadjustable. For instance, machines in swash plate construction, in whichthe absorption volume is adjusted by adjusting the pivoting angle of theswash plate, can be used.

To adjust the absorption volume of the first hydraulic motor 55 orsecond hydraulic motor 56, a control valve 32′, which can take a firstand a second switch position which are identical to the first and secondswitch position of the control valve 32 from FIG. 1, is provided.Additionally, the control valve 32′ can take a third switch position,and is continuously adjustable. The control valve 32′ is controlled viathe electromagnet 34, and in the opposite direction by a furtherelectromagnet 34′. The further electromagnet 34′ is controlled by anadditional signal line 35′ from the electronic device 36. If, becausethe driving lever 37 is steered in the direction of forward motion F, acorresponding signal is transmitted via the further signal line 38 tothe electronic device 36, in the shown embodiment current is supplied tothe further electromagnet 34′ by means of the additional signal line35′, and the control valve 32′ is in its first switch position.

In the first switch position, the removal duct 40 is connected to thefirst control pressure duct 39. On the other hand, the second controlpressure duct 49 is relieved via the relief duct 50 into the tank volume11.

The first hydraulic motor unit 5′ and the second hydraulic motor unit 6′are constructed identically. The first hydraulic motor unit 5′ has, aswell as the adjustable first hydraulic motor 55, which drives the firstdriven shaft 20, a variation device 30′. The variation device 30′consists essentially of a set pressure regulating valve 51 as thecontrol valve, and an adjustment device 53. The adjustment device 53acts on an adjustment mechanism of the first hydraulic motor 55, andadjusts its absorption volume. The adjustment device 53 includes apretensioning spring 57, which applies a force to a set piston 59, andadjusts the first hydraulic motor 55 in the direction of maximumabsorption volume. Oppositely to the pretensioning spring 57, in a setpressure chamber 61 a hydraulic force acts on the set piston 59. Themagnitude of the hydraulic force on the set piston 59 can be adjusted bychanging the pressure in the set pressure chamber 61 via the setpressure regulating valve 51.

For this purpose, the set pressure regulating valve 51 can becontinuously adjusted between a first and a second final position. It ispressed by a set pressure regulating valve spring 26′ in the directionof its first final position. In this first final position of the setpressure regulating valve 51, the set pressure chamber 61 is connectedvia a set pressure joining duct 65 to a tank duct 67, which relieves theset pressure chamber 61 into the tank volume 11.

Oppositely to the force of the set pressure regulating valve spring 26′,a hydraulic force acts on the set pressure regulating valve 51 on thecontrol surface 28′ if a pressure is fed via the first control pressureduct 39. In the first switch position of the control valve 32′, thecontrol surface 28′ is pressed by the auxiliary pump 9 via the firstcontrol pressure duct 39, which is connected to the removal duct 40. Theset pressure regulating valve 51 is adjusted in the direction of itssecond final position, in which a set pressure duct 63 is connected tothe set pressure joining duct 65. The set pressure joining duct 63 isconnected to the third connecting duct 8′, so that in this finalposition the set pressure chamber 61 is pressed with the pressure of thesecond main duct 8. The increasing pressure in the set pressure chamber61 moves the set piston 59 against the force of the pretensioning spring57, and thus adjusts the first hydraulic motor 55 in the direction of asmaller pivoting angle.

Simultaneously, the second control pressure duct 49 is connected to therelief duct 50 by the control valve 32′, so that the pressure which isapplied to the control surface 29′ is relieved into the tank volume 11.The set pressure regulating valve 52, as the control valve of the secondhydraulic motor unit 6′, is therefore, because of the set pressureregulating valve spring 27′, in its first final position, in which theset pressure chamber 62 of the adjustment device 54 of the variationdevice 31′ of the second hydraulic motor unit 6′ is connected to thetank volume 11 via a set pressure joining duct 66 and a tank duct 68.The second hydraulic motor unit 6′ is thus adjusted in the direction ofa large pivoting angle.

Similarly to the example from FIG. 1, in a first switch position of thecontrol valve 32′ the hydraulic motor unit 5′ is adjusted so that asmaller torque acts on the first driven shaft 20, which in turncorresponds to the front axle of the vehicle, than on the second driveshaft 21. If the driving lever 37 is now moved from the position forforward motion F into a position for backward motion R, this newposition is converted by the electronic device 36 into correspondingcontrol signals for the electromagnets 34, 34′. Current no longer flowsthrough the further electromagnet 34′, instead current flows via thesignal line 35 through the electromagnet 34, which adjusts the controlvalve 32′ in the direction of its second switch position. In the secondswitch position, the removal duct 40 is connected to the second controlpressure duct 49, and the first control pressure duct 39 is connected tothe relief duct 50. In this way, again similarly to the embodiment fromFIG. 1 and the adjustment described above of the hydraulic motor units5′ and 6′, the second hydraulic motor unit 6′ is adjusted in thedirection of smaller absorption volume, and the first hydraulic motorunit 5′ is adjusted in the direction of greater absorption volume. Thechange of the absorption volume of the first hydraulic motor unit 5′ andsecond hydraulic motor unit 6′ is again preferably equally great.

Additionally, the control valve 32′ can take a third switch position. Inthe third switch position, both the first control pressure duct 39 andthe second control pressure duct 49 are connected to the removal duct40. To take the third switch position, both electromagnets 34, 34′ arecontrolled correspondingly by the electronic device 36, if it isdetected that the operator has specified a high driving speed.Specifying a high driving speed can be detected by the electronic device36 because the driving lever 37 passes a specified position. The thirdswitch position of the control valve 32′ corresponds to a fast gear. Inthis position, both the first hydraulic motor unit 5′ and the secondhydraulic motor unit 6′ are adjusted in the direction of a smallerpivoting angle. In this way the transmissible torque is reduced, butsimultaneously the r.p.m. of the first and second hydraulic motor 55 and56 for a given delivery volume of the pump 2 is increased, resulting ina higher speed of the driven vehicle.

For both the control valve 32′ and the control pressure regulating valve51 and 52, continuous adjustment between the final positions can beprovided, so that the absorption volume of both the first hydraulicmotor 55 and the second hydraulic motor 56 is continuously adjustable.

In FIG. 3, an embodiment of the controller according to the invention,in which instead of the driving lever 37 from FIG. 1 an inclinationsensor 70 is provided, is shown. The inclination sensor detects theinclination of the vehicle relative to the level. If the inclinationsensor 70 detects that the level of the front axle is above the level ofthe rear axle, the electronic device 36 does not supply current to theelectromagnet 34, and the control valve 32 is in its first switchposition, which is fixed by the control valve spring 33. In this switchposition of the control valve 32, as was explained in detail about FIG.1, the first hydraulic motor unit 5 is adjusted in the direction ofsmaller torque, and thus the torque on the front axle is preventivelyreduced.

On the other hand, if the vehicle is in a situation in which the levelof the rear axle is higher than the level of the front axle, theelectronic device 36 switches a current onto the electromagnet 34, whichthen brings the control valve 32 into its second switch position. In thesecond switch position, the torque of the second drive shaft 21 isreduced by switching off the second hydraulic motor 23′ of the secondhydraulic motor unit 6.

The absorption volume of the hydraulic motor units 5 and 6 is adjustedsolely on the basis of the detected inclination of the vehicle. In thisway, corresponding to the procedure from FIG. 1, before slip occurs onthe front or rear axle, the absorption volume of the first hydraulicmotor unit 5 and second hydraulic motor unit 6 can be adjusted so thatthe tendency to form slip is reduced. Use of the inclination sensor 70makes it possible to apply a smaller torque to the up-side axle. Bypreventive adjustment of the absorption volume of the first hydraulicmotor unit 5 and second hydraulic motor unit 6, because of a simplesignal of the inclination sensor 70 a distribution, which is adapted tothe driving situation, of the torque on the first driven shaft 20 andsecond driven shaft 21 is made possible.

In FIG. 3, an inclination sensor 70, which has only two switch positionsfor the two different inclination directions, a so-called inclinationsensor, is enough. However, use of the gradient sensor 70 is notrestricted to the embodiment according to FIG. 3, but can also, incombination with the variable adjustment possibility of FIG. 2, make itpossible to adapt the torque distribution to the relevant gradient. Forthis purpose, an inclination sensor 70 which outputs a continuous signaldepending on the inclination is provided.

In FIG. 4, a further example of a controller according to the inventionis shown. In this, instead of direction of motion or gradient signal,the ratio of the pressure in the first main duct 7 and second main duct8 is used for control. The first hydraulic motor unit 5 and secondhydraulic motor unit 6 are identical with those from FIG. 1, and wereexplained in detail there. In this embodiment, pressure is applied tothe first control pressure duct 39 and second control pressure duct 49,or they are connected to the tank volume 11, by a control valve unit 80instead of the control valve 32.

The control valve unit 80 comprises a selection valve 81 and a reliefvalve 82. On the input side, the selection valve 81 is connected via afirst main duct branch 83 to the first main duct 7, and via a secondmain duct branch 84 to the second main duct 8. The first main ductbranch 83 is also connected to a first measurement surface 85, throughwhich a force is applied to the selection valve 81, counteracting ahydraulic force which acts on a second measurement surface 86. Togenerate a hydraulic force on the second measurement surface 86, thesecond measurement surface 86 is connected to the second main ductbranch 84. Additionally, on the selection valve 81, selection valvesprings 91 are provided. One selection valve spring in each case exertsa force on the selection valve 81 in the direction of the first andsecond measurement surface 85 and 86. If the pump 2, for instance, inthe case of the forward motion described with reference to FIG. 1,delivers into the second main duct 8, the pressure in the second mainduct 8 exceeds the pressure in the first main duct 7. Correspondingly, agreater pressure is delivered via the second main duct branch 84 to thesecond measurement surface 86 than to the first measurement surface 85.With such a pressure gradient, the selection valve 81 is in its firstswitch position, shown in FIG. 4. In this first switch position of theselection valve 81, a connection is made between the first main ductbranch 83 and a first output 87 of the selection valve 81. On the otherhand, the connection between the second main duct branch 84 and thesecond output 88 of the selection valve 81 remains interrupted.

The relief valve 82 has a first input 89 and a second input 90. Thefirst input 89 is connected to the first output 87 of the selectionvalve 81, and the second input 90 is connected to the second output 88of the selection valve 81. Also, the first control pressure duct 39 isconnected to the first input 89 of the relief valve 82. The secondcontrol pressure duct 49 is connected to the second input 90 of therelief valve 82.

In the described first switch position of the selection valve 81, thefirst input 89 of the relief valve 82 and thus also the first controlpressure duct 39 are connected to the first main duct branch 83. A thirdmeasurement surface 93, through which a hydraulic force which isdirected oppositely to a hydraulic force which acts on a fourthmeasurement surface 94 is applied to the relief valve 82, is alsoconnected to the first control pressure duct 39. The fourth measurementsurface 94 is connected to the second control pressure duct 49. Becauseno pressure is applied to the second control pressure duct 49 in thedescribed first switch position of the selection valve 81, the pressurewhich acts on the third measurement surface 93 brings the relief valve93 into a first position, in which the second input 90 of the reliefvalve 82 is connected via a further tank duct 95 to the tank volume 11.

Accordingly, in the first position of the relief valve 82 the secondcontrol pressure duct 49 is connected to the tank volume 11, and thefirst control pressure duct 39 is connected via the first main ductbranch 83 to the first main duct 7.

In the case of a pressure reversal in the first main duct 7 and secondmain duct 8, the selection valve 81 is brought into a second switchposition, in which the second main duct branch 84 is connected to thesecond output 88, so that a control pressure is applied via the secondcontrol pressure duct 49 to the control surface 29 of the control valve25 of the second hydraulic motor unit 6. The control pressure istherefore the pressure of the main duct 7 or 8 which is lower, but isstill clearly above the pressure level of the tank volume 11. Byconnecting the second output 88 to the second main duct branch 84, ahydraulic force is applied to the fourth measurement surface 94, andbrings the relief valve 82 into its second position. In the secondposition, the first input 89 is connected via the further tank duct 95to the tank volume 11, so that the control surface 28 of the controlvalve 24 of the first hydraulic motor unit 5 is relieved.

The adjustment of the hydraulic motors on the basis of the pressures onthe control surfaces corresponds to the explanations of FIG. 1.

The selection valve 81, and consequently the relief valve 82, areswitched solely on the basis of the sign of the pressure differencebetween the first main duct 7 and the second main duct 8. This meansthat even without the occurrence of slip during motion on the level, thechange of direction of motion, through a corresponding pressure changein the first and second main duct 7 and 8, results in an adaptation ofthe distribution of the torques. Since the sign of the pressuredifference is used exclusively, a pressure reversal is also detected ifit is caused, for instance, by downhill motion. The control valve unit80, irrespective of the direction of motion of the vehicle, adjusts thehydraulic motor unit which is oriented to the up-side to a smallerabsorption volume.

To reduce the length of the required joining ducts, it is also possibleto integrate a control valve unit 80 in each of the two hydraulic motorunits 5, 6. The pressures, which are required for control, of the firstmain duct 7 and second main duct 8 are present there in any case.

In FIG. 5, a combination of the control valve unit 80 from FIG. 4 withthe adjustable hydraulic motor units 5′ and 6′ from FIG. 2 is shown. Inthis embodiment, all the valves which are used can be adjustedcontinuously between their final positions.

In FIG. 6, an extension of the controller according to the inventionfrom FIG. 4 is shown. As an extension, between the selection valve 81and the relief valve 82 an over-control valve 100, which in an idleposition defined by an over-control valve spring 101 connects the firstoutput 87 of the selection valve 81 to the first input 89 and the secondoutput 88 of the selection valve 81 to the second input 90 of the reliefvalve 82, is shown.

The over-control valve 100 can be brought into an over-control position,in which additionally the first input 89 and the second input 90 of therelief valve 82 are connected to each other, by an over-control magnet102. In this way, the lower pressure of the main ducts 7 or 8 is appliedto both the first control pressure duct 39 and the second controlpressure duct 49, and thus both the first hydraulic motor unit 5 and thesecond hydraulic motor unit 6 are adjusted for smaller absorptionvolume. With constant delivery volume of the pump 2, the result is alower torque with simultaneously increased driving speed.

Because of the pressure which is equally present on the third and fourthmeasurement surface, the relief valve takes a central, third position.The first input 89 and second input 90 are connected to the tank volume11 via the tank duct 95. The connection takes place choked. Theconnection enables a small quantity of oil from the low-pressure-sidefirst or second main duct 7 or 8 to enter the tank volume 11, thusachieving additional cooling.

In FIG. 7, an example of a vehicle which is equipped with a controlleraccording to the invention is shown. The vehicle 105 is a road rollerwith a front roller 106 and a rear roller 107. The front roller isdriven by the first hydraulic motor unit 5 or 5′ and the rear roller 107is driven by the second hydraulic motor unit 6 or 6′. To specify thedirection and speed of motion, the driving lever 37 is provided. Tosimplify operation during work, a second driving lever 37′ is provided,so that a driving lever is available to the operator on both sides of adriver's seat 109.

1. A controller for a hydrostatic traversing mechanism with at least one hydraulic pump, which is connected via a first and a second main duct to a first hydraulic motor unit which drives a front axle and a second hydraulic motor unit which drives a rear axle, the absorption volume of the first and the second hydraulic motor unit being adjustable via a first and a second variation device respectively, and a direction of motion being specified as a forward motion (F) or backward motion (R) by a position of driving lever, wherein the first and second variation device are controlled by a control valve, the control valve taking a first switch position in the case of forward motion (F) being defined by the position of the driving lever and a second switch position in the case of backward motion (R) being defined by the position of the driving lever, in the first switch position the first variation device being controlled so that the first hydraulic motor unit is adjusted in the direction of smaller absorption volume, and in the second position the second variation device being controlled so that the second hydraulic motor unit is adjusted in the direction of smaller absorption volume.
 2. A controller for a hydrostatic traversing mechanism with at least one hydraulic pump, which is connected via a first and a second main duct to a first hydraulic motor unit which drives a front axle and a second hydraulic motor unit which drives a rear axle, the absorption volume of the first and the second hydraulic motor unit being adjustable via a first and a second variation device respectively, and with an inclination as uphill inclination or downhill inclination, wherein the first and second variation device are controlled by a control valve, the control valve—taking a first switch position in the case of downhill inclination, in the first switch position the first variation device being controlled so that the first hydraulic motor unit is adjusted in the direction of smaller absorption volume, and in the second position the second variation device being controlled so that the second hydraulic motor unit is adjusted in the direction of smaller absorption volume,
 3. The controller according to claim 1 or 2, wherein in the first switch position of the control valve a control pressure is applied to a control surface of a control valve of the first variation device, and a control surface of a control valve of the second variation device is connected to a tank volume, and in the second switch position of the control valve the control surface of the control valve of the first variation device is connected to the tank volume, and the control pressure is applied to the control surface of the control valve of the second variation device.
 4. The controller according to claim 1 or 2, wherein the control pressure is generated by an auxiliary pump.
 5. The controller according to claim 1 or 2, wherein the control valve is a 4/2-way valve.
 6. The controller according to claim 1 or 2, wherein the control valve is a 4/3-way valve.
 7. According to claim 6, wherein in a third switch position, the control surfaces of the control valves of the first and second variation device are connected to the tank volume.
 8. The controller according claim 1 or 2, wherein the control valve is actuated electromagnetically.
 9. The controller according to claim 1 or 2, wherein the first and second hydraulic motor unit each include at least two hydraulic motors, of which at least one can be switched on and off to change the absorption volume of the hydraulic motor unit.
 10. The controller according to claim 1 or 2, wherein the first and second hydraulic motor unit each include an adjustment motor.
 11. The controller according to claim 10, wherein the control valve is continuously adjustable between the first and second switch position.
 12. The controller according to claim 11, wherein the control valves are continuously adjustable between two final positions.
 13. The controller for hydrostatic traversing mechanism with at least one hydraulic pump, which is connected via a first and a second main duct to a first hydraulic motor unit which drives a rear axle, the absorption volume of the first and the second hydraulic motor unit being adjustable via a first and a second variation device, wherein the first and second variation device are controlled by a control valve unit, the control valve unit taking a first or second switch position depending on the sign of the pressure difference between the first and second main duct, and in the first switch position the first variation device being controlled so that the first hydraulic motor unit is adjusted in the direction of smaller absorption volume, and in the second position the second variation device being controlled so that the second hydraulic motor unit is adjusted in the direction of smaller absorption volume.
 14. The controller according to claim 13, wherein the control valve unit includes a selection valve and a relief valve, and that in a first switch position of the selection valve a first input of the relief valve is connected to the first main duct, the first or second main duct which is connected to the relief valve being the one with lower pressure.
 15. The controller according to claim 14, wherein a control surface of a control valve of the first variation device is connected to the first input of the relief valve, and that a control surface of a control valve of the second variation device is connected to the second input of the relief valve.
 16. The controller according to claim 15, wherein the relief valve is switched into a first or second position depending on the pressure which is present at a first or second input, in the first position the second input being connected to a tank volume, and in the second position the first input being connected to the tank volume.
 17. The controller according to claim 13, wherein the first and second hydraulic motor unit each include at least two hydraulic motors, of which at least one can be switched on and off to change the absorption volume of the hydraulic motor unit.
 18. The controller according to claim 13, wherein the first and second hydraulic motor unit each include an adjustment motor.
 19. The controller according to claim 18, wherein the selection valve and relief valve are continuously adjustable between appropriate final positions.
 20. The controller according to claim 19, wherein the control valves are continuously adjustable between two final positions.
 21. The controller according to claim 13, wherein between the selection valve and the relief valve an over-control valve, which in its idle position connects a first and second output of the selection valve to the first input and second output of the relief valve, and which in an over-control position connects both outputs of the selection valve to both inputs of the relief valve, is provided.
 22. The controller according to claim 21, wherein the relief valve is in a third position if the over-control valve is in its over-control position, and in the third position of the relief valve its first and second input are connected to the tank volume.
 23. The controller according to one of claim 13, wherein one control valve unit is integrated into each of the first hydraulic motor unit and second hydraulic motor unit.
 24. The controller according to claim 1, 2, or 13, wherein the change of the absorption volume of the first and second hydraulic motor unit in the direction of smaller absorption volume is compensated for by a corresponding change of the absorption volume of the other hydraulic motor unit in the direction of greater absorption volume. 